THIS invention relates to self-steering bogies for rail vehicles and in particular to the provision of inter-axle shear stiffness in self-steering bogies.
Inter-axle shear stiffness for self-steering bogies is commonly provided by means of cross-anchors which are fitted to the wheelset sub-frames, as proposed for instance in the known Scheffel cross-anchor design, or by means of A-frames which are connected to one another, at their apices, on the transverse centre line of the bogie, as proposed for instance in the known List Steering Arm design. However, on irregular track, and particularly at points and crossings, high shock loads are exerted on the wheelsets and transmitted to the sub-frames or A-frames. The frames must therefore be robust. Robustness is also necessary to ensure that the forces transmitted to the frames do not generate unduly high force couples on the journal roller bearings of the bogie wheelsets which could shorten the service life of those bearings. The required robustness results in heavy sub-frames or A-frames which considerably increase the unsprung wheelset mass and this can in turn reduce the hunting stability of the bogie at high speeds.
It is however understood that the inter-axle shear forces which are required to ensure effective wheelset guidance for hunting stability and curving performance are only a fraction, typically no more than 30%, of the shock forces encountered at points and crossings.
Against this background the present invention proposes to provide an apparatus which will limit the transmission of shear forces between the wheelsets to a level at which adequate hunting stability and curving performance can be attained but which will nevertheless be acceptable to the wheel journal roller bearings.
According to one aspect of the invention there is provided an inter-axle shear stiffening apparatus for a self-steering rail bogie having axle structures including axles which are journalled in axle box bearings, the apparatus comprising arms which are rigidly connected or connectable to respective axle structures of the bogie to extend towards one another from the axle structures in generally fore and aft directions, and lateral force transmitting means for acting between the arms to transmit lateral forces between them while accommodating relative lateral movement between the arms, wherein, irrespective of the extent of relative movement between the arms, the lateral force transmitting means is only capable of transmitting between them lateral forces of limited, predetermined magnitude which provide the bogie with inter-axle shear stiffness to enhance hunting stability of the bogie but are insufficient to impose excessive force couples on the axle box bearings.
According to another aspect of the invention there is provided a self-steering rail bogie having axle structures including axles journalled in axle box bearings and including an inter-axle shear stiffening apparatus as summarised above, with the arms of the apparatus rigidly connected to the axle structures and the apparatus providing inter-axle shear stiffness to enhance the hunting stability of the bogie.
Other advantageous and preferred features of the invention are set forth in the appended claims.